Slight fibrosis of organ or tissue be called fibrosis, severe fibrosis can cause damage of tissues leading to organ scarring. Tissue fibrosis is not only in lung and liver, but in all the organs and systems of the human body. A variety of factors (such as inflammation, immune response, poison, ischemia and changes of hemodynamics, and so on) cause parenchymal cellular damage. This leads to parenchymal cells inflammation, deformation, necrosis, and activates the corresponding macrophages to release cytokines and growth factors which in turn activate the resting extracellular martrix (ECM) to produce cells, and then transform the cells into myofibroblasts. Myofibroblasts proliferate and secrete cytokines which act on macrophages through paracrine. Myofibroblasts can synthesize a lot of collagen of ECM. ECM degradation is decreased at the same time causing organ and tissue fibrosis. Therefore, the occurrence and development of organ and tissue fibrosis is a result of the interactions between multiple factors, such as cell, cytokine and ECM. Cell produced by ECM is important for the formation of organ or tissue fibrosis. Therefore, one of the drug targets for treating organ and tissue fibrosis is the cell produced by ECM. Therapeutic goal can be achieved by inhibiting the cell proliferation, activation and inducing the cell apoptosis.
It is because each organ or tissue has different functions, morphologies and different main component cells, different organ or tissue fibrosis have commonness and individuality in the pathogenesises. Cells can be produced by ECM, while hepatic stellate cells are produced in liver, glomerular mesangial cells are produced in glomerulus, renal interstitial fibroblasts are produced in renal interstitium, lung fibroblasts are produced in lung, cardiac fibroblasts are produced in heart and peritoneal mesothelial cells are produced in peritoneal. Therefore, there are some differences in the pathogenesises and therapeutic targets of different organs or tissues fibrosis.
An anti-fibrotic drug named pirfenidone (PFD, 5-methyl-1-phenyl-2-(1H)-pyridone) was disclosed in patent EP1138329A. Experiments show that PFD could prevent ECM gathering, or even reverse it in animal experiments of renal fibrosis, pulmonary fibrosis, and in clinical trials of patients with specific lung fibrosis.